1. Field of the Invention
The present invention relates to a chassis for a chair seat that allows adjustment in an inclination angle of the backrest relative to the seat and that provides a reliable arrangement for adjustment.
2. Description of the Related Art
A typical chassis for a chair seat is shown in FIGS. 7 and 8 and includes a swivel seat 1', a connecting seat 2', a spring seat 3', an adjusting rod 4', and a connecting rod 5'. The swivel seat 1' includes a number of holes 11' in comer areas thereof for connection with the chair seat 6', a hole 12' in a mediate portion thereof for connection with the spring seat 3', and lateral holes 13' and 14' through which the adjusting rod 4' and the connection rod 5 extend, respectively. The connecting seat 2' includes a hole 21' through which a pneumatic rod 7' extends. The connecting seat 2' further includes lateral holes 22' and 23' through which the adjusting rod 4' and the connection rod 5 extend, respectively. The connecting seat 2' further includes a hole 24' for mounting the spring seat 3'. The spring seat 3' includes a sleeve 32', a spring 31' partially mounted in the sleeve 32', and a threaded rod 33' that extends through the hole 12' in the swivel seat 1' and securely engages with a lower end of the sleeve 32'. The adjusting rod 4' includes an end 41' extended through the lateral hole 13' to restrain swivel movement of the swivel seat 1'. The adjusting rod 4' further includes a pressing section 42' to press against an' upper end of the pneumatic rod 7' to adjust the level of the chair seat 6'.
Although the seat 6' and the backrest 8' can be swiveled due to provision of the spring 31', the inclination angle of the backrest 8' relative to the seat 6' cannot be fixed. In addition, as shown in FIG. 9, the user might fall from the chair when the rearward motion of the backrest 8' goes too far, since the seat 6' swivels together with the backrest 8'.